Technical Field
The present invention relates to an improvement in a raw material vaporizing and supplying apparatus for semiconductor manufacturing equipment using so-called metalorganic chemical vapor deposition (hereinafter, referred to as MOCVD), and, also, to a raw material vaporizing and supplying apparatus equipped with a raw material concentration detection mechanism, capable of controlling a raw material concentration of a raw material mixed gas supplied to a process chamber highly accurately and quickly, and also capable of displaying the raw material gas concentration in real time.
Description of the Related Art
Conventionally, as this type of raw material vaporizing and supplying apparatus for semiconductor manufacturing equipment, a raw material vaporizing and supplying apparatus which utilized a so-called bubbling method has been used in many applications. In vaporizing and supplying of a raw material according to the bubbling method, there has been a strong demand for, such as, realizing significant downsizing of the raw material vaporizing and supplying apparatus, an increased supply quantity of a raw material, quick and highly accurate control of a mixture ratio of carrier gas and raw material gas, and direct display of a raw material gas concentration in the mixed gas supplied to a chamber.
Therefore, various types of research and development have been made for the bubbling-type raw material vaporizing and supplying apparatus. For example, techniques in the fields of controlling a flow rate of a mixed gas supplied to a process chamber and a raw material gas concentration in the mixed gas are disclosed in Japanese Published Unexamined Patent Application Publication No. H07-118862, Japanese Patent No. 4605790, etc.
FIG. 6 is a drawing that describes the structure of a reaction gas control method described in Japanese Published Unexamined Patent Application Publication No. H07-118862 given above. In FIG. 6, reference numeral 31 denotes a closed tank, 32 denotes a heater, 33 denotes a mass flow controller, 34 denotes an injection pipe, 35 denotes an ejection pipe, 36 denotes a mass flow meter, L0 denotes a liquid raw material (TEOS, or tetraethyl orthosilicate), GK denotes a carrier gas (N2), Gm denotes a mixed gas (G+GK), G denotes a raw material gas, Q1 denotes a carrier gas flow rate, Q2 denotes a raw material gas flow rate, QS denotes a mixed gas flow rate, 37 denotes a flow rate setting circuit, 38a denotes a concentration calculation circuit, 38b denotes a concentration setting circuit, 38c denotes an electric current control circuit, QS0 denotes a set flow rate, and KS0 denotes a set concentration.
The present invention is to control a temperature of the liquid raw material L0, thereby regulating a produced flow rate Q2 of a raw material gas G to keep the concentration of the raw material gas G in a mixed gas Gm constant. More specifically, computation is made for the produced flow rate Q2 of the raw material gas with reference to a mixed gas flow rate QS from the mass flow meter 36 and a carrier gas flow rate Q1 from the mass flow controller 33.
Further, the thus computed Q2 (the produced flow rate of the raw material gas) is used to determine Q2/QS, thereby computing a raw material gas concentration KS in the mixed gas Gm.
The thus computed raw material gas concentration KS is input into the concentration setting circuit 38b and by comparing with a set concentration KS0, a difference between them (KS0−KS) is subjected to feedback to the electric current control circuit 38c. Where such a relationship of KS0>KS is obtained, the heater 32 is operated so as to raise its temperature, thereby increasing the produced flow rate Q2 of the raw material gas G. Where such a relationship of KS0<KS is obtained, the heater is operated so as to lower its temperature, thereby decreasing the produced flow rate Q2.
Further, the mixed gas flow rate QS from the mass flow meter 36 is compared with the set mixed gas flow rate QS0 on the flow rate setting circuit 37, thereby regulating the flow rate Q1 from a mass flow controller so that a difference between them becomes zero.
However, the method for regulating the raw material gas concentration as shown in FIG. 6 increases the produced flow rate Q2 of a raw material gas by heating the liquid raw material L0, (or decreases the produced flow rate Q2 of the raw material gas by lowering a temperature of the liquid raw material L0). Therefore, there is a problem that the method is very low in response characteristics with respect to regulation of concentration and extremely low in response characteristics with respect to a decrease in concentration of the raw material gas.
Further, the mass flow meter (thermo-flowmeter) 36 undergoes a great fluctuation in measured flow rate value when a type of mixed gas Gm or a mixture ratio thereof is changed. Therefore, the method shown in FIG. 6 has such a problem that, irrespective of whether a type of mixed gas Gm is changed or the type is the same, a great change in a mixture ratio (concentration of raw material gas) will result in a drastic decrease in the measuring accuracy of a flow rate QS.
Still further, the change in temperature of heating the liquid raw material L0 will raise a pressure inside the closed tank 31, thereby inevitably resulting in a fluctuation in primary side pressure of the mass flow meter 36. As a result, the mass flow meter 36 will have an error in the measured flow rate value, thus revealing a problem of decreasing the control accuracy of a flow rate and concentration of raw material gas.
On the other hand, FIG. 7 is a drawing which shows the structure of a raw material gas supplying apparatus of Patent No. 4605790 which has been described above. The apparatus is able to supply a mixed gas having a predetermined concentration of raw material gas to a process chamber, with a flow rate thereof being controlled highly accurately with high responsive characteristics.
In FIG. 7, reference numeral 21 denotes a closed tank, 22 denotes a constant temperature device, 23 denotes a mass flow controller, 24 denotes an injection pipe, 25 denotes an ejection pipe, 26 denotes an automatic pressure regulator for the closed tank, 26a denotes an arithmetic and control unit, 26b denotes a control valve, L0 denotes a liquid raw material, GK denotes a carrier gas, Q1 denotes a carrier gas flow rate, G denotes a raw material gas, Gm denotes a mixed gas (G+GK), and QS denotes a mixed gas flow rate.
In the raw material gas supplying apparatus, first, the constant temperature device 22 is used to heat the closed tank 21, a main body of the automatic pressure regulator 26 for the closed tank and a piping line L to a predetermined temperature. Thereby, an internal space of the closed tank 21 is filled with saturated steam (raw material gas) G of a raw material.
Further, the carrier gas GK at a flow rate Q1 controlled by the mass flow controller 23 is released from a bottom of the closed tank 21. A mixed gas Gm of the carrier gas GK and the saturated steam (or vapor) G of the raw material is supplied through the control valve 26b of the automatic pressure regulating device 26 to outside (process chamber).
The mixed gas Gm is regulated for the flow rate QS by controlling a pressure of the mixed gas in the closed tank 21 by the automatic pressure regulator 26. A set flow rate QS0 is compared with a computation flow rate QS computed with reference to measurement values obtained from a pressure gauge P0 and a temperature gauge T0 at an arithmetic and control unit 26a of the automatic pressure regulator 26. And, the control valve 26b is opened and closed so that a difference between them (QS0−QS) becomes zero, thereby controlling a flow rate QS of supplying the mixed gas Gm to a set flow rate QS0.
The raw material gas supplying apparatus shown in FIG. 7 is able to supply the mixed gas Gm having a constant raw material gas concentration which is determined in response to a heating temperature of the liquid raw material L0 by regulating an internal pressure of the closed tank, with a flow rate thereof controlled highly accurately with high response characteristics, thereby providing excellent effects of controlling a flow rate of the mixed gas having a predetermined and constant raw material gas concentration.
Although the raw material gas supplying apparatus is able to measure a flow rate QS of the mixed gas Gm highly accurately and with high response characteristics, it has a basic problem that the mixed gas Gm is not measured for a raw material gas concentration highly accurately and cannot display a measurement value thereof. As a matter of course, if a heating temperature of the closed tank 21, a flow rate of the carrier gas GK, a level height of the raw material liquid L0, etc., are determined, it is possible to estimate a raw material gas concentration KS in the mixed gas Gm to some extent. However, a technique has not yet been developed that a raw material gas concentration of the mixed gas Gm supplied to a process chamber can be continuously and automatically measured and displayed without using a complicated and expensive concentration meter, etc., in a less expensive and economical manner.